why snow fairy cant traverser, croix the border, while in the 1st movie they came to pixie dust tree?

i watched Tinkerbell: Secret of The Wing last month.
And today i watch La Fée Clochette 1st movie.
i am little confused. in the Secret of The Wing, snow fairy cant traverser, croix the Border. But why in 1st movie Cera (snow fairy, i know her name in La Fée Clochette Lost Treasure NDS) and minister of winter came to the pixie dust arbre when La Fée Clochette looked for her talent?